A typical process of fabricating a semiconductor element including a post-shaped connection terminal (hereinafter, also referred to as a “post” for the sake of convenience) includes the following series of steps. First, a barrier metal layer is formed on a pad (e.g., an aluminum pad) of a semiconductor substrate, and a plating resist is patterned to expose the pad (barrier metal layer) therefrom. Then, a post-shaped connection terminal (post) is formed on the barrier metal layer by plating (e.g., electrolytic copper plating). Thereafter, the plating resist is removed, and an exposed portion of the barrier metal layer is etched. The shape of the post obtained in this process is columnar in many cases.
An example of the related art is described in Patent document 1 (Japanese Laid-open Patent Publication No. 5-218138).
A semiconductor element having a post-shaped connection terminal is mounted on a wiring board by flip-chip bonding. FIG. 1B illustrates an example of mounting a semiconductor element (chip) 10a having post-shaped connection terminals (posts) 16 on a wiring board 20. Here, solder 26 is attached to the connection terminal (onto the pad 22) of the board, and then, the leading end 16a of the post 16 of the chip is brought into contact with the solder 26. Thereafter, the solder 26 is melted by heating and then solidified (flip-chip bonding). During this processing, the following inconveniences occur where the shape of the post 16 is columnar in particular.
First, the solder 26 melted during the heating crawls up on the surface 16b of the post 16 from the leading end 16a thereof due to the surface tension in many cases, although depending upon the amount of the attached solder 26. In this case, the solder 26 which has crawled up on the side surface is highly likely to form a bridge between the adjacent posts 16, to thereby cause a short circuit, although depending upon the arrangement interval (pad pitch) between the posts. In the example illustrated in FIG. 1B, a “short circuit” has occurred between the two posts 16 on the right side. Moreover, even with the solder 26 crawling up on the post 16 only slightly, where the amount of the solder 26 to be attached is large, the post 16 is likely to push out the solder 26, thus still causing a short circuit to occur between the adjacent solders 26.
Meanwhile, in the case where the solder does not crawl along the side surface of the post (e.g., when the amount of the solder to be attached onto the pad is small), there arises another problem. Namely, the surface area of a portion of the post where the solder is in contact (which corresponds to the surface area of the leading end 16a of the post 16 or less in the example illustrated in FIG. 1B) becomes small as compared with the case where the solder crawls up on the side surface. AS a result, the connection reliability between the chip and the board is lowered, and an open failure is likely to occur in this case.
Moreover, in the flip-chip bonding, the solder 26 needs to be connected to the post 16 by heating and melting the solder 26 with the leading end 16a of the post 16 brought into contact with the solder 26, and then appropriately pushing the post 16 into the solder 26. However, if the posts 16 are not pushed enough, all of the posts 16 are not always brought into contact with the solder 26 because the respective heights of the solders 26 on the pads 22 of the board 20 vary. Meanwhile, if the posts 16 are pushed more than enough, the solder 26 spreads around each pad 22, and thus a bridge is formed between the adjacent solders 26. For this reason, there is a problem in that it is difficult to set an appropriate amount of the push for the post 16.
The problems mentioned above appear more notably in the semiconductor elements which are made to have a narrower pitch between pads (terminals) in particular.